This invention relates to aqueous dispersions comprised of water-soluble polymers, processes for making said dispersions, and methods of using said dispersions in water treating, dewatering, water clarification, papermaking, oil field, soil conditioning, food processing, mineral processing, and biotechnological applications.
U.S. Pat. No. 4,380,600 discloses a process for producing an aqueous dispersion of water-soluble polymers. The aqueous dispersion may contain inorganic salt. However, the aqueous dispersions exemplified therein have disadvantageously high bulk viscosities.
U.S. Pat. No. 4,673,704 and EP 0 170 394 A2 disclose products comprised of particles above 20 microns in size of a high molecular weight polymer gel interconnected by a continuous phase that is an aqueous solution of an equilibrating agent that holds the water content of the particles in equilibrium with the water content of the aqueous phase and that prevents substantial agglomeration of the particles in the fluid product. Although these references are entitled "Aqueous Polymer Dispersions," the products disclosed therein are distinguished from the aqueous dispersions of U.S. Pat. No. 4,380,600 and from the aqueous dispersions of the instant invention in that the particles of U.S. Pat. No. 4,673,704 and EP 0 170 394 A2 are not generally held suspended in a continuous matrix of the aqueous phase but instead generally rest substantially in contact with one another but slide over one another. A process for dispersing the polymer gel into an aqueous solution of an equilibrating agent and working the polymer while in that medium is disclosed in U.S. Pat. No. 4,778,836 and EP 0 169 674 B1. Also, U.S. Pat. No. 4,522,968 discloses a process for dispersing certain powdered water-soluble homopolymers or copolymers in an aqueous solution containing a polymer of ethylene oxide and/or propylene oxide.
U.S. Pat. Nos. 4,929,655 and 5,006,590 disclose processes for preparing aqueous dispersions of water-soluble polymers by polymerizing benzyl-containing monomers in the presence of an organic high molecular multivalent cation and a multivalent anionic salt. The benzyl group-containing monomer may be replaced by a hydrophobic alkyl group-containing monomer as in EP 0 525 751. Numerous references concern these and similar polymers, e.g. U.S. Pat. Nos. 5,332,506; 5,332,507; 5,330,650; 5,292,793, 5,435,922; 5,466,338; EP 0 595 156 A1; EP 0 630 909 A1; EP 0 657 478 A2; EP 0 629 583 A2; EP 0 617 991 A1, EP 0 183 466 B1, EP 0 637 598 A2; EP 0 717 056 A2; JP 61-6396; JP 61-6397; JP 61-6398; JP 62-262799; JP 64-15130; JP 2-38131; JP 62 15251; JP 61-138607; Hei 6-329866; and JP 62-100548. Although some of the aqueous dispersions in these references have relatively low bulk viscosities, the need to include special monomers containing aromatic or hydrophobic alkyl groups in order to render the polymer insoluble in salt solution may be disadvantageous because the special monomers may be expensive and dilutive of the polymer effect in a specific application.
The effect of salts on the solubility of various substances in aqueous solution is well discussed in the scientific literature. The "Hofmeister" series ranks anions according to their ability to increase or decrease the solubility of substances in water. Although positions in the ranking may vary slightly, depending on the substance, a generally accepted ranking of the anions is: EQU Salting-out SO.sub.4.sup.2-.about.HPO.sub.4.sup.2- &gt;F&gt;Cl.sup.- &gt;Br.sup.- &gt;I.sup.-.about.ClO.sub.4.sup.- &gt;SCN.sup.- Salting-in (kosmotropic) (chaotropic)
Kosmotropic salts generally decrease the solubility of substances in water. For instance, the Hofmeister ranking apparently guided the choice of salts for precipitating cationic water soluble polymers, containing hydrophobic groups, in U.S. Pat. Nos. 4,929,655 and 5,006,590, as well as EP 0 630 909 A1, EP 0 525 751 A1, and EP 0 657 478 A2, as evidenced by their use of strongly kosmotropic salts containing sulfate and phosphate anions. On the other hand, chaotropic salts generally increase the solubility of substances in water.
There are numerous means known to those skilled in the art for determining whether a particular salt is kosmotropic or chaotropic. Representative salts which contain anions such as sulfate, fluoride, phosphate, acetate, citrate, tartrate and hydrogenphosphate are kosmotropic. Representative salts which contain anions such as thiocyanate, perchlorate, chlorate, bromate, iodide, nitrate and bromide are chaotropic. The chloride anion is generally considered to be at about the middle of the Hofmeister ranking, being either weakly chaotropic or weakly kosmotropic, depending on the particular system. In the instant invention, although occasionally chaotropic, inorganic salts which contain the chloride anion tend to be kosmotropic.
Small amounts of sodium thiocyanate, for instance about 0.1% by weight, on total, have been reported to be useful as stabilizers for polymer dispersions as in EP 0 657 478 A2, where (NH.sub.4).sub.2 SO.sub.4 was used to deposit the polymer. Sodium thiocyanate and sodium iodide have been reported to be useful as stabilizers for hydroxylamine-containing water-soluble polymer systems, as in EP 0 514 649 A1. U.S. Pat. No. 3,234,163 teaches that small amounts of thiocyanate salts, preferably 0.1 to 1 percent, based on the weight of the polymer, are useful for stabilizing polyacrylamide solutions.
The Hofmeister ranking has been observed in solutions of high molecular weight, water-soluble polymers. For instance, the effect of various salts on the solubility of synthetic, water-soluble polymers was explored by Shuji Saito, J. Polym. Sci.: Pt. A, Vol. 7, pp. 1789-1802 (1969). This author discussed the effect of various anions on polymer solubility and stated "This anionic order seems to be independent of the type of counter cations and is in line with Hofmeister's lyotropic series for anions." Similarly, in M. Leca, Polymer Bulletin, Vol. 16, pp. 537-543, 1986, the viscosity of polyacrylamide, as determined in 1N solutions of various salts, was found to increase in the order HPO.sub.4.sup.2- &lt;H.sub.2 O&lt;Br.sup.- &lt;NO.sub.3.sup.- &lt;I.sup.- =BrO.sub.3.sup.- &lt;ClO.sub.3.sup.- =SCN.sup.-. The viscosities were reported to be higher in more chaotropic salt solutions than in less chaotropic, or kosmotropic, salt solutions. Certain novel cationic polyelectrolytes, termed ionene polymers, were reported (D. Casson and A. Rembaum, Macromolecules, Vol. 5, No. 1, 1972, pp. 75-81) to be insoluble in either 0.4 M potassium iodide or 0.4 M potassium thiocyanate. It has also been reported (W-F. Lee and C-C. Tsai, J. Appl. Polym. Sci., Vol. 52, pp. 1447-1458, 1994) that poly(trimethyl acrylamido propyl ammonium iodide) did not dissolve in 0.5 M Na.sub.2 ClO.sub.4 or 0.5 M NaNO.sub.3.
Certain anionic organic salts, such as hydrotropes and surfactants, also tend to increase the solubility of substances in water. However, poly(allylammonium chloride) was reported (T. Itaya et al., J. Polym. Sci., Pt. B: Polym. Phys., Vol. 32, pp. 171-177, 1994, and references 3, 5 and 6 therein; also Macromolecules, Vol 26, pp. 6021-6026, 1993) to precipitate in solutions containing the sodium salt of p-ethylbenzenesulfonate, p-propylbenzenesulfonate or naphthalenesulfonate. Poly(4-vinyl pyridine) quaternized with butyl chloride and poly(allylammonium chloride) were reported (M. Satoh, E. Yoda, and J. Komiyama, Macromolecules, Vol. 24, pp. 1123-27, 1991) to precipitate in solutions of NaI and also in solutions containing the sodium salt of p-ethylbenzenesulfonate, respectively. Compositions comprising sulphonated hydrocarbon surfactants and hydrophilic cationic polymers were disclosed in U.S. Pat. No. 5,130,358. Mixtures of chaotropic salts, or anionic organic salts, and kosmotropic salts may be used to precipitate cationic polymers as in U.S. application Ser. No. 08/725,436, filed even date herewith.
Aqueous dispersions of water-soluble polymers are disclosed in U.S. Pat. Nos. 5,403,883; 5,480,934; 5,541,252; EP 0 624 617 A1; EP 0 573 793 A1; and WO 95/11269. A problem remains in that the aqueous dispersions exemplified in these references still have relatively high bulk viscosities.
A process for preparing crosslinked copolymer beads from water-soluble monomers in an aqueous solution containing an inorganic salt and a dispersant is disclosed in U.S. Pat. No. 5,498,678 and EP 0 604 109 A2. Mixtures of aqueous dispersions and water-in-oil emulsions are disclosed in Hei 7-62254 and Hei 6-25540. The addition of a nonionic surfactant and an oleaginous liquid to an aqueous dispersion to maintain flowability is disclosed in U.S. Pat. No. 5,045,587. Mixtures of cationic polymers are disclosed in Sho-52-71392 and homogeneous blends of water-soluble polymers are disclosed in U.S. Pat. No. 4,835,206 and EP 0 262 945 B1. Bimodal cationics for water clarification are disclosed in U.S. Pat. Nos. 4,588,508 and 4,699,951. Blends of water-in-oil polymer emulsions are disclosed in U.S. patent application Ser. No. 08/408,743.
In spite of the effort to make satisfactory aqueous dispersions, the problem remains of producing aqueous dispersions of high molecular weight water soluble polymers that have advantageously low bulk viscosities, high active solids content, minimal quantities of dilutive material, and that dissolve readily and can be prepared with a broad range of cationicity.